The purpose of a door operator is to open and close a door. Automatic door operators are used on public buildings and residences to allow for access by the physically disabled or where manual operation of the door may be inconvenient to users. In public facilities, it is a required American National Standard for doors that provide ingress and egress to have the ability to open automatically in order to allow handicapped people passage through the doorway.
A variety of electro-mechanical automatic door operators are known. A typical door operator includes an electric motor and a linkage assembly for operatively coupling the drive shaft of the motor to a door so that the door will be opened and closed when the drive shaft rotates. Activation of the door operator is initiated by means of an electric signal generated in a variety of ways such as, for example, a pressure switch, an ultrasonic or photoelectric presence sensor, motion sensors, radio transmitters, wall switches, and the like. The door may then be closed under power or with a door closer. A conventional door closer uses an internal spring mechanism which is compressed during the opening of the door for storing sufficient energy so that the door can be returned to a closed position without the input of additional electrical energy. In the some door operators, the automatic, powered opening system is still engaged once the closing sequence starts, and consequently the spring force of the door closer must overcome the resistance caused by counter-rotating the gear train coupled to the motor. Since this spring force must be large, an individual manually opening the door must exert substantial force to overcome the spring force and the resistance forces generated by the opening system. Moreover, driving the components of the powered opening system during manual opening and closing of the door causes the gear train to become worn more quickly over time.
Some door operator systems are provided with clutch mechanisms between the motor and the linkage assembly that enable the door to be moved freely under manual power. Door operators with clutch mechanisms may provide some level of safety when objects are in the door's pathway of movement. Various clutch mechanisms decouple powered opening systems during the closing cycle, which is particularly necessary in the event of an interruption of power supply or when an obstacle is encountered. Some require a sensor mounted in the motor housing or drive shaft to sense stoppage of the door by an obstacle and to disengage the clutch or stop the motor so as to prevent damage to the device or obstacle. This solution still presents problems. For example, a door operator utilizing a slip clutch or the like will create some drag or resistance when the door is manually opened or closed. Moreover, conventional clutch mechanisms that do not create resistance suffer from a limited range of motion.
Other known automatic door operator systems enable a user to open the door under automatic power or under manual power, and the systems use a predetermined, elapsed time in between opening and closing sequences. Under automatic power, a motor is operated by a controller and opens at a particular speed and direction. The motor may then stall or rest for the fixed, predetermined period. At the expiration of such time period, the controller then signals the motor to reverse direction and close the door under power. Under manual operation, the door is opened by the user. Once the user releases the door, which may be before the door has reached the fully open position, the controller may direct the motor to continue to open the door until reaching the fully open position, despite that the user may have already moved through the doorway. This operation may not be desirable in cases where the door is an outside door and the weather conditions cause considerable heat loss in the winter or heat gain in the summer. Moreover, security at building entrances may be a concern. Automatic door operator systems that delay return of a manually opened door to the closed position beyond the time needed for a person to move through the doorway create a heightened security risk, as there may be an extended opportunity for entry by an unauthorized person.